1. Field of the Invention
This invention relates to protective covers or rain caps used to cover an outlet of an exhaust stack of an internal combustion engine when the engine is idling or stopped. The rain cap opens the outlet when exhaust pressure increases and the vehicle is moving. More particularly, the invention relates to an improved rain cap that uses aerodynamic forces arising from air flow past the rain cap to move the cap and open the outlet. A fuel-efficient aerodynamic profile is presented to the air flow by the rain cap when the outlet is opened.
2. Brief Description of the Prior Art
Rain caps for diesel and gasoline internal combustion engines have been known for use on construction equipment, farm tractors and over-the-road tractor trucks. All of these vehicles use upstanding exhaust pipes or stacks projecting vertically from the manifolds of the engine. Rain or weather caps protect the internal parts of the internal combustion engines from moisture. Absent such a cap, the equipment, which often sits for extended periods of time, could accumulate moisture from rain and snow entering the engine from the exhaust stack. An open exhaust valve is all that is necessary for the engine to fill with water and develop rust or a hydrostatic lock, often resulting in a bent connecting rod when the engine is started.
More recently, over-the-road diesel tractor trucks have a water trap formed by extending the exhaust below the manifold, which makes it extremely difficult for water to enter the engine. The main purpose of rain or weather caps has therefore been to keep the exhaust pipe from accumulating moisture, rather than the engine. The interior of a modern diesel truck exhaust pipe is coated with unburned carbon. Upon starting of the engine, any loose carbon is ejected from the pipe and deposited on the truck cab and any trailer connected to the truck. Preventing moisture from entering the stack decreases the amount of carbon loosened by moisture and lowers the maintenance cost associated with cleaning the trucks.
Current rain caps, exemplified by the prior art patent to R. McClain (U.S. Pat. No. 4,059,045), are pivotally mounted about an axis that does not pass through the exhaust pipe. A clamp is mounted on the end of the exhaust pipe and pivotally mounts the cap. The two major disadvantages to such a cap are the excessive back pressure the engine must overcome, resulting in lost fuel efficiency, and the clattering noise that is made as these caps open and shut while the engine idles. An improved cap, such as seen in E. Janke (U.S. Pat. No. 4,495,859), is quieter but still provides a high back pressure during operation.
A weather cap which slides within the exhaust stack under the influence of exhaust pressure is seen in R. Hopkins (U.S. Pat. No. 3,446,010). A pivotal type cap opened by exhaust temperature heating a bimetal strip is seen in R. Jasensky (U.S. Pat. No. 4,205,706). Exhaust pressure is used to move a vane located in the exhaust stack to release a latch and allow the exhaust to open the weather cap in W. Janke (U.S. Pat. No. 3,964,376). The Janke cap cannot be opened from the outside and only opens upon exhaust pressure being applied thereto.
It has been found that the ideal configuration for the outlet of an exhaust stack is one wherein the end of the pipe or stack is cut at a 45.degree. angle from front to back to define an oval rather than circular outlet opening. This angle provides a minimum back pressure to the engine, resulting in improved fuel efficiency. A rain or weather cap cannot be mounted on such an exhaust pipe under any prior art known.
None of the prior art patents show a weather cap in combination with the ideal exhaust stack outlet design for minimizing back pressure. None of the prior art disclose an aerodynamically operated weather cap.